# E&M Lecture Videos Spring 2020

Videos of lectures on electricity and magnetism by Dr. Ruth Chabay, Spring 2020.
Lecture 1: Beginning of Electric & Magnetic Interactions; review of 3D vectors and the vector form of Coulomb’s law, in part in support of those students who did not have the Matter & Interactions course on mechanics.
Lecture 2: The field concept; gravitational field; calculating the field produced by electric charges.
Lecture 3: Review the electric field of a point charge; the strong form of the superposition principle (the net field is the vector sum of the fields contributed by all the charges in the surroundings and the contribution by any charge to the field is unaffected by the presence of other charges); the field of an electric dipole; approximating the dipole field; retardation when the charges no longer exist.
Lecture 4: Review of dipoles; net charge; conservation of charge; conductors and insulators; polarizing an atom; 1/r5 dependence of the force of an induced dipole on a point charge.
Lecture 5: Conventions for drawing diagrams representing polarized objects; conductors; salt water as a conductor; electric field goes to zero in a conductor in equilibrium; metals and the electron sea; the Drude model and average drift speed; grounding; charging by induction; tinyurl.com/SurfaceCharge used to show the computed equilibrium surface charge distribution on a polarized block of metal.
Lecture 6: Exploring the pattern of electric field made by distributed charges; the electric field of a long thin uniformly charged rod; divide the rod into 4 equal-length pieces and calculate the field on the midplane, treating the pieces as point charges; algebraic analysis leading to an integral; checking the result (units, field far from the rod); approximate result near the rod (E proportional to 1/r) but not near an end of the rod; summary of the procedure.
Lecture 7: Calculating the electric field of a uniformly charged ring, disk, and capacitor; International Space Station video of charged droplets orbiting a charged plastic knitting needle.
Lecture 8: Review of potential energy; electric potential; sign issues; electric field is the negative of the gradient of the potential.
Lecture 9: Calculating the electric potential in nonuniform electric fields; the electric potential at a point in space; the round-trip path integral of the electric field made by stationary charges is always zero.
Lecture 10: Magnetic field; the Biot-Savart law; right-hand rule; detecting and measuring magnetic field with a compass; the Biot-Savart law is valid in your own rest frame; magnetic field contributed by currents; equilibrium and steady state; electron current nAv; conventional current enAv.
Lecture 11: Comments about frame dependence and about retardation; electron current and conventional current; adding up the contributions to the magnetic field of many current-carrying elements of a conductor; calculating the magnetic field of a long straight current-carrying wire; the magnetic field of a current-carrying ring, which is a magnetic dipole; magnetic dipole moment; the source of magnetic field in a magnet can be thought of in terms of currents at the atomic level.
Lecture 12: Some issues related to attendance and homework; a microscopic view of DC circuits in terms of charge and field; the feedback mechanism that establishes the steady state; a gradient of surface charge produces a uniform electric field; proof that the electric field inside a wire is uniform both along the wire and over a cross section of the wire.
Lecture 13: Review the snaky circuit, the loop rule, and the node rule; low-conductivity Nichrome wire in a circuit; circuit analysis in the microscopic context of electric field and mobile charges; non-Coulomb force in a battery; emf; a circuit with thick and thin Nichrome wires in series; voltage measurements on some simple battery-and-bulb circuits, including series and parallel circuits.
Lecture 14: High-resistance and low-resistance light bulbs in series; electrostatic effects of surface charge in a 10,000 volt circuit; capacitors in circuits; capacitance.
Lecture 15: Macroscopic view of circuits; conductivity; resistance; conventional circuit element representations; analysis with the familiar loop and node rules; power; series and parallel resistors.

At this point the course had to be converted to an on-line course due to the coronavirus emergency of Spring 2020.

Lecture 16: Real batteries; ammeters and voltmeters; RC circuits; circuit review.
Lecture 17: Magnetic force; circular motion in a magnetic field; magnetic force on a current-carrying wire; mass spectrometer.
Lecture 18: Motional emf; magnetic torque; Alice and Bob and Einstein.
Lecture 19: Patterns of field in space; Gauss’s law for electricity; Gauss’s law for magnetism. The computer visualization programs can be run at matterandinteractions.org/student.
Lecture 20: Using Gauss’s law to prove some important properties of electric field; Ampere’s law; using Ampere’s law to calculate magnetic field.
Lecture 21: Faraday’s law; video demonstration of Faraday’s law; direction of the curly electric field; calculating the magnitude of the effect.
Lecture 22: Completing the four Maxwell equations; demo of electromagnetic radiation lighting a bulb; propagation of electromagnetic radiation with configuration of electric and magnetic fields that are consistent with Maxwell’s equations.
Lecture 23: The source of electromagnetic radiation is accelerated charges; numerical calculations; 1/r beats 1/r2 at large distances; relationship between classical electromagnetic radiation and quantum photons.
Lecture 24: The effects of electromagnetic radiation on matter; re-radiation; waves; interference; index of refraction.
Lecture 25: Sparks in air; exploring various models for how sparks form; testing the models; ruling out some models as being clearly wrong.